An itch for discovery

Scientists have gotten their nails into an area that has long been out of reach — the pathways that make people want to scratch.

Itching and scratching aren’t hard to understand. The skin is the largest organ of the body and it is in constant contact with the world. Something is bound to irritate it, and when that happens, people and animals are bound to scratch.

A label inside of a polo shirt collar can cause a day of neck wriggling. A mosquito bite can send our fingers into a clawing frenzy.

Whatever the cause … sunburns, diseases, allergic reactions to food … itching occurs when something sets off the nerves in our skin and warning signals travel through the spinal cord and on to the brain.

Like its cousins … tickle and pain … the itch is a defense mechanism. But instead of eliciting a giggle or a rapid retreat from a hot stove, itching has the remarkable effect of making us want to dig into our flesh.

Until recently, scientists did not even scratch the surface of the molecular mechanisms of itching. But researchers with the National Institutes of Health studying mice have discovered a special bio-circuit that the brain uses to transmit the itch signal.

The pathway relies on a tiny molecule that plugs into specific nerves located in the spinal cord. In absence of the molecule, the circuit was broken.

Mice did not respond to a number of substances that normally would make them scratch, even though other sensory communication, such as temperature sensitivity or pain, was not affected.

Scientists believe humans have the same unique itch response and mechanism that mice have. If so, drugs tailored to block the itching circuit could spell relief for millions of people with eczema, psoriasis and other chronic conditions.

More research is needed, but the days of the wicked itch may well be numbered.